The biology of behavior is a diversified, exciting field in which C. Kung and his colleagues have promoted the ciliated protozoan, Paramecium, as an organism of great merit for involving genetic probes in electrophysiological studies. Paramecium is proving to be a useful model for excitable cells such as nerves and muscles. This proposal suggests expansion of genetic studies and ultrastructural analyses of phenotypes to complement electrophysiological and biochemical analyses currently being pursued in other laboratories with the ultimate goal of elucidating mechanisms of action of excitable membranes. The proposed genetic studies focus on the selection of new types of behavioral mutants including second step mutations (changing the phenotype of known behavioral mutations) and genetic characterization of these mutants. Selective techniques for obtaining these mutants are described. Freeze-fracture ultrastructural studies of ciliary membranes of wild type and mutant stocks of paramecia will be continued and extended. New results point to specialized arrays of membrane particles, the plaques, as having alterations correlated with certain behavioral phenotypes. The extent to which plaque variation follows single gene-controlled modification of behavior will be determined. Other membrane particle arrays such as the ciliary necklace will be studied as appropriate. The discovery that plaques may vary from wild type in some mutants leads to the proposal that cells regenerating cilia following deciliation should be studied for behavioral and ultrastructural phenotypes.